Hubble repair mission
14 Hubble’s giant mirror was very nearly its downfall. Initial images from the telescope were disappointing, and the fault was traced to the mirror’s grinding and polishing process – one lens used to check the shape was out of position.
The response to this was a 1993 servicing mission, STS-61, that had been scheduled to go to the telescope for maintenance anyway. An instrument called the Corrective Optics Space Telescope Axial
Replacement or COSTAR was added to Hubble, replacing one of its original instruments. As corrective optics, it was essentially giving the telescope glasses.